1. Field of the Invention
The invention relates to electromagnetic transmission devices, and more particularly to electromagnetic transmission devices with reduced electrical power consumption.
2. Description of the Related Art
Microminiature image capturing devices are commonly applied in cellular phones, computers, vehicle radars, video game players, and medical inspection devices, etc. The microminiature image capturing devices have been developed to provide high definition quality, reduced power consumption, low manufacturing costs, and reduced size. As such, actuators disposed in the microminiature image capturing devices, for moving lens modules thereof, are critical.
Automatic displacement driving devices applied in lens modules may employ drivers providing rotational power with a rotational axis thereof paralleling an optical axis of the lens modules or drivers providing movement power with a moving direction thereof paralleling the optical axis of the lens modules.
An example of a driver providing rotational power with a rotational axis thereof paralleling an optical axis of a lens module is a stepping motor. The driver requires additional transmission-conversion mechanisms to enable the lens module to move along the optical axis. When the lens module arrives at a final position, no electricity is required to maintain the lens module therein. However, the driver has many components. Thus, the structure of the driver is complicated, and the size thereof cannot be reduced.
An example of a driver providing movement power with a moving direction thereof paralleling an optical axis of a lens module is a voice coil motor, a piezoelectric actuator, or a liquid lens actuator. The driver directly adjusts the position of the lens module. Compared with the driver providing rotational power, this driver has fewer components and is small. Nevertheless, there is a need to further reduce the size, manufacturing costs, and power consumption of this driver.
Referring to FIG. 1, U.S. Pat. No. 6,856,469 discloses a conventional lens drive device with a magnetic member 9, a spacer member 12, and a spring member 50 arranged parallel to an optical axis of a lens 2. The lens 2 is retained at retaining positions by magnetic attraction between a drive magnet 6 and the magnetic member 9 and by the spring member 50. The magnetic member 9 requirement, however, increases the number of constituent elements of the lens drive device, such that manufacturing costs and overall size of the lens drive device cannot be reduced. Additionally, electrical power is required to retain the lens 2 at the retaining positions, and the relationship between the moving position of the drive magnet 6 and magnetic member 9 and the variation of magnetic force thereof is nonlinear. Accordingly, positioning control of the lens 2 in the conventional lens drive device is difficult.
Additionally, as shown in FIG. 2A and FIG. 2B, Japan Patent Publication No. 2005-128405 discloses a conventional lens drive device 1. An upper spring 9 and a lower spring 11 enable precise movement of a lens module (including a lens 20, an upper cover 24, a lower washer 17, a coil 15, and a lens supporting base 7) and reduce friction during movement thereof. The upper spring 9 and lower spring 11 may be regarded as extensions of the coil 15, serving as conductors at ends thereof. Grooves 37 on an upper frame 23 and ribs 31 on the lens supporting base 7 bear impact or vibration generated by contact between a moving assembly (including the lens 20, upper cover 24, lower washer 17, coil 15, and lens supporting base 7) and a stator (including the upper frame 23, a yoke 3, and a magnet 13), maintaining a deviation value of the moving assembly with respect to an optical axis within an acceptable range and preventing excessive rotation of the lens 20 from adversely affecting other mechanisms in the lens drive device 1. Specifically, the yoke 3 enhances overall permeability of the lens drive device 1, increasing a magnetic voice coil force for moving the lens module. The yoke 3, however, adversely affects reduction of manufacturing costs and overall size of the lens drive device 1.
Hence, there is a need for electromagnetic transmission devices with reduced electrical power consumption, size, and manufacturing costs.